The present invention generally relates to a method of making a liquid smoke composition from the condensable products resulting from the fast pyrolysis of wood or cellulose and, more particularly, to a method of making a high browning liquid smoke composition. The high browning liquid smoke composition of this invention may be used to color and flavor edible foodstuffs.
Use of liquid smoke solutions as a replacement for smoking food by direct contact with wood smoke has become a standard industry practice. When applied to the surface of meats, proteinaceous foodstuffs and food casings, liquid smoke will give the food a characteristic smoke flavor and produce a dark smoked color. The achievement of a smokehouse-like product by application of a liquid smoke solution to food requires controlling and balancing many related variables such as the food composition, the temperature and humidity, the processing and contact time, and the amount and concentration of smoke solution applied.
For example, when applying a liquid smoke solution to a meat, the processor normally must compromise the smoke color or browning of the meat to keep the flavor at a desired level because the flavor imparting ability of known liquid smoke solutions is generally too intense at a desired smoked color. There is a need in the industry for a liquid smoke solution with good coloring or browning properties that has acceptable flavoring properties.
Liquid smoke is a complex and variable mixture of chemicals produced during pyrolysis and includes many compounds, some of which are normally liquid at room temperature. Pyrolysis is a general term for the thermal decomposition of any organic matter, such as wood, plants, or fossil fuels, which occurs either during combustion or in the absence of combustion. Combustion uses the oxidation or burning of a portion of the organic matter to provide the thermal energy required to vaporize and decompose the remainder of the matter. For pyrolysis without combustion, thermal energy must be supplied indirectly from an external source, such as radiation, solid, or gaseous heat carriers, or from thermal conduction through reactor walls. The externally supplied thermal energy vaporizes and decomposes the organic matter without directly oxidizing or burning it.
Either method of pyrolysis produces condensable liquids, non-condensable gases and solids in varying proportions depending upon reaction conditions. The condensable liquids from pyrolyzed wood can be further sub-divided into water soluble organics and water insoluble tars. It is known that the desirable active ingredients for flavoring foodstuffs found in smoke solutions are among the water soluble organics.
The production of commercially produced liquid smoke solutions typically begins with smoke made by pyrolysis and limited combustion of wood. After pyrolysis or combustion, the smoke is subsequently collected and fed through a column countercurrent to the flow of recirculating water. The resulting dilution of the condensable smoke components in water results in the removal of undesired tars and water insoluble components; however, further refinement of the liquid solution is needed for the food flavoring or coloring applications described above. A typical commercial liquid smoke preparation for surface applications to foodstuffs is the liquid smoke flavoring described in U.S. Pat. No. 3,106,473 to Hollenbeck.
Current conventional pyrolysis methods are characterized by relatively slow thermal reactions which occur at moderate temperatures. In a typical commercial process for example, wood feedstock, generally dried ground sawdust, is fed into a pyrolysis system at elevated temperatures. The sawdust is maintained at these temperatures for more than one minute. These conventional pyrolysis methods suffer from relatively poor yields of liquid smoke products which have less than desired browning or flavoring properties.
Improved pyrolysis products may be obtained using fast or flash pyrolysis methods. Fast pyrolysis methods employ extremely fast heating rates and short material and vapor residence times to yield high quality liquid smoke compositions. The heating rate for fast or flash pyrolysis may be greater than 1000.degree. C. per second and vapor residence times may be less than 2 seconds. The liquid smoke solutions produced by fast pyrolysis methods are generally preferred to liquid smoke solutions made using conventional pyrolysis methods. A method of making fast pyrolysis liquid smoke is described in U.S. Pat. No. 4,876,108 and the related divisional application Ser. No. 07/358,650 filed May 26, 1989. The entire contents of both applications are incorporated by reference herein.
The color and flavor chemistry of liquid smoke compositions is highly complex as evidenced by the over four hundred compounds identified as constituents of these compositions. A summary of the many constituents found in liquid smoke is listed by Maga in "Smoke in Food Processing" CRC Press, pp. 61-68 (1968).
Although there are hundreds of different chemical species present in liquid smoke, the species are generally divided into five classes based on chemicals having distinct functional groups. The five classes generally are acids, carbonyls, phenols, basics and neutrals. A majority of researchers skilled in the art of smoke solutions have concluded that phenols are primarily flavoring and aroma compounds, carbonyls are mainly responsible for surface coloration, and acids are principally preservatives and pH controlling agents. Acids and carbonyls also make a secondary contribution to flavor and may enhance the surface characteristics of smoked meat products.
A representative commercial liquid smoke product, for example, with a titratable acidity level of about 11% contains about 13% carbonyls, about 1.5% phenols, and at least 70% water. The remaining constituents, about 4.5% of the total mass balance of the smoke, include basic and neutral organic compounds.
Where surface coloring is important, measuring the amount of active carbonyls in a solution may determine the browning or coloring properties of a liquid smoke composition. The active carbonyls are believed to initially react with the available amino groups on surface proteins of a foodstuff. Subsequent reactions occurring under drying and heating conditions lead to the formation of the characteristic brown smoked color. The concentration of a specific carbonyl species, hydroxyacetaldehyde, is also a good indicator of the coloring or browning potential of a liquid smoke solution.
Another measurement that is used to characterize liquid smoke is the browning index defined according to procedures described below. The browning index is also used in the smoke flavoring industry to measure the browning or coloring performance of a liquid smoke solution.
Liquid smoke solutions may be used to color and flavor comestible food products by treating the food in a variety of ways. The application of liquid smoke may be done on individual items in batch or continuous modes by spraying on dipping. For large batches, an atomized cloud of liquid smoke may be used. In addition, sausages, bologna and hams may be processed in casings into which liquid smoke solutions have been incorporated.